Solvent extraction



April 5,1966 A. c. MGKINNIS 3,244,761

` SOLVENT EXTRACTION Filed July 31, 1961 MKE-UP 50A VEA/7' MA KE-u .sumem" A40/warms 59 United States Patent O 3,244,761 SOLVENT EXTRACTIONArt C. McKinnis, North Long Beach, Calif., assignor to Union Oil Companyof California, Los Angeles, Calif., a corporation f California FiledJuly 31, 1961, Ser. No. 128,243 20 Claims. (Cl. 2643-674) This inventionrelates to a solvent extraction method Ifor separating hydrocarbons ofgreater aromaticity from hydrocarbons of lesser aromaticity in admixturetherewith. More specifically, the invention relates to such a method inwhich mixtures of amines and acids are employed as selective solventsfor the hydrocarbons of greater aromaticity. The invention hasparticular futility for the recovery of diaromatic hydrocarbons, such asnaphthalene or the like, from mixtures thereof with monoaromatichydrocarbons of substantially equivalent boiling points, such as alkylbenzenes or the like.

There are a number of known solvent extraction procedu-res for isolatingvarious components of hydrocarbon mixtures and numerous materials havebeen proposed for use as selective solvents in such procedures,typically representative of which are sulfur dioxide, furfura-l,diethylene glycol, nitriles, organic bases, etc. Such solvent extractionprocedures have been attempted with varying deg-rees of success onmixtures of aromatic yand nonaromatic hydrocarbons for purposes ofextracting .all of the aromatics therefrom, but heretofore it has notbeen possible to bring about any kind of effective fractional separationof the aromatic components from each other by solvent extraction means.

I have now discovered an improved method of solvent extraction for useon hydrocarbon mixtures whereby aromatic components of differing degreesof aromaticity can be economically and effectively fractionated.

There are many hydrocarbon mixtures, as, 'for example, various petroleumprocessing fractions, which contain substantial proportions ofdiaromatic hydrocarbons such as naphthalene and its alkyl and polyalkylderivatives, and also monoaromatic hydrocarbons which can be monocyclic,such as alkyl benzenes, and/or bicyclic, such as alkyl tetralins, alkylindanes, alkyl indenes and the like, which boil Within the same boilingrange as the diaromatics. Tlhe boiling range of the diaromatics inhydrocarbon mixtures of this type is typically from about 400 to about450 F. A speci-fic example of such a hydrocarbon mixture is the heavyreformate Ifraction obtained in the catalytic reforming of naphtha orheavy Agasoline fractions. This fraction normally boils above about 400F. and contains from about 40 to about 8O percent by weight naphthaleneand methyl naphthalenes, the remainder being either la-rgely made up ofmonoaromatic com-A 3,244,761 Patented Apr. 5, 1.966

in the diaromatic, monoaromatic, etc., categorie-s by conventionalfractionation means. For one thing, the like boiling point ranges of thediaromatics and monoaromatics normally found in such mixtures precludesthe possibility of getting effective separation between these twoclasses of materials by fractional distillation techniques. The presentinvention comprises a method of solvent extraction employing a uniqueamine-acid solvent by means of which segregation of aromatics of thesame degree of aromaticity is readily and economically feasible.

In addition to the problem of separating like boiling aromatics ofdiffering degrees of'aromaticity, there is a parallel problem ofseparating aromatics from nonaromatics of like Aboiling ranges. Thereare many such mixtures, exemplary of which are those petroleum fractionsknown to contain monoaromatics, such as polyalkyl benzenes, boilingwithin the yrange vfrom about 400 to about 450 F., as well asnonaromatics such as paraflins and naphthenes of the same boiling range.Here again,

as in the case of the like boiling aromatics, fractional distillationfails as a practical means of accomplishing the desired separation andthe solvent extraction method of this invention furnishes a simple andpractical solution to the problem.

It is thus a principal object of this invention to provide an improvedsolvent extraction method by means of which componential ,fractions ofvarious aromaticity levels can be segregated from mixtures of sucharomatic compounds.

It is another object of the invention to provide a solvent extractionmethod for readily and economically separating aromatic compounds fromlike boiling nonaromatic compounds in admixture therewith.

A more specific object of the invention is to provide an economicalsolvent extraction method by means of which diaromatic compounds arereadily separable lfrom like boiling monoaromatic compounds in admixturetherewith. Other objects and advantages of the invention will beapparent from the complete description thereof which follows. 7

The degrees of aromaticity of organic compounds of roughly equivalentboiling points depend upon the number of aromatic rings (-benzenenuclei) in their respective" molecules, the higher the number of suchrings the greater the aromaticity of a given compound. Thus diaromaticcompounds, those having two aromatic rings per molecule, are conside-redto have a greater degree of aromaticity than the monoaromatic compoundswhich have molecular structures containing only one such ring. It makeslittle difference, insofar as degree of aromaticity is concerned,

Whether polyaromatic compounds have individual or condensed ringsystems. Thus, diaromatics of individual ring systems such as biphenyl,diphenylmethane, etc., are considered to have roughly the same degree ofaromaticity as the dinuclear aromatics (diaromatics having condensedring systems), such as naphthalene, etc., at least insofar as thisinvention is concerned.

The method of this invention is not limited to the treatment of organicmixtures in which the aromatics of highest possible degree of4arom-aticity are diaromatics,A

and mixtures containing higher polyaromati-c compounds are also amenableto separation -by said method. For example, it is Within the scope ofthe invention to subject hydrocarbon mixtures containing triar-omaticcom-y pounds, such as vanthracene and pheneanthrene, and diaromaticcompounds of roughly the same boiling point level to solvent extractionas taught herein, to separate the triaromatics from `the diaromatics.

The method of this invention is not limited in application to thetreatment of organic mixtures having clearly obvious differences indegree of aromaticity among its various components. There are manyorganic mixtures containing -aromatic components not sharplydistinguishable from others present in degree of aromaticity and thetreatment of such grey area mixtures either for the separat-ion of thearomatics in toto or for further separation `of said aromatics intofr-actions of varying degrees of aromaticity, lies within the purview ofmy invention. It is more difficult to separate such grey area aromaticsinto distinct fractions than 4it is `to separate more sharply black andwhite aromatics, such as diarom-atics and monoaromatics, but su-chseparations are possible and hence within the scope of my invention.Among the above-noted grey area aromatic compounds of intermediatedegrees of aromaticity may be mentioned those substituted aromatioscontaining functional groups of such nature as to have a :significanteffect of one sort or another on the aromatic-ity of their-unsubstituted counterparts. It will be clear that a wide variety offeed mixtures can be resolved by the method taught herein.

Attention is now directed Lto the accompanying drawings whichschematically illustrate typical processes for the Ipractice of myinvention.

Turning first to FIGURE l, there is shown a continuous countercurrentsolvent extraction process employing a solvent of the type describedmore fully hereinafter, such as for example, an azeo-tropic mixture o-ftriethylamine and acetic acid. A feed stream containing both aromaticand nonaromatic hydrocarbons of like boiling ranges such as a heavyreformate petroleum fraction containing diaromatics '(naphthalene,alkylated naphthalenes, ete); monoaromatics (alkyl benzenes, alkyltetralins, alkyl indanes, etc); and nonaromatics (naphthenes andparans), is continuously fed into the bottom of a countercurrent solventextraction column .1 through line 3 as shown. Simultaneously, solvent isrecycled into the top of column 1 through line 5, from a sourcehereinafter disclosed. Solvent extraction column 1 is so designed andthe conditions of operation so fixed and controlled as lto result in theextraction of substantially all of the aromatic components from thefeedstock as it circulates upward in countercurrent contact with thesolvent in said column.

As -those skilled in the art realize, there are generally four importantthings to be considered in the practice of countercurrent solventextraction, namely: (l) the operating temperature; (2) the operatingpressures; (3) the number of extraction stages; and `(4) thesolvent/feed ratio. Careful selection and control of operatingconditions in the above -four areas is important in order to achieveoptimum phase separation, selectivity, and solvent power, all of 'whichhave a bearing on product yield and purity.

The operating temperature level is important in solvent extractionoperations -since in Ithe usual case too low a temperature results in aninordinately high feed viscosity which in turn results in unnecessarilylong phase separation periods. Additionally, too low a temperature isundesirable in that it normally has a detrimental effect on the solventpower of selective solvents. On the other hand, excessively hightemperatures are undesirable since they u-sually have the effect ofreducing solvent selectivity and tend -to make the extract and raffinatephases mutually misc-ible. Where solvent extraction is carried out atatmospheric pressure, the operating temperatures should preferably notexceed `the boiling points of any of the various components present inthe system since this would obviously have a deleterious effect on theoperation.

Reasons have been given why extremes of temperature in either directionare undesirable in solvent extraction CII operations. However, theeffects of lowering the operating te-mperature below a certain level arenot necessarily all bad since such lowering frequently results in anincrease of solvent selectivity. Furthermore, not all of the effects ofan excessive elevation of temperature are necessarily deleterious, since`such elevation normally brings about a shortening of the time requiredfor lphase separation as well as an improvement in the solvent power ofselective solvents. It will be apparent from the abovenotedconsiderations that the selection of an optimum temperature range forsolvent extraction purposes depends on many factors and entails abalancing of the advantages and disadvantages inherent in varioustemperature adjust-ments, taking into consideration the characteristicsof the components present in the system, the operating pressures, etc.So too, the selection of optimum operating pressures for solventextraction operations is subject to the consideration of other factorsof an influencing nature. rl`hus operating pressures can vary fromsubatmospheric, Ithrough atmospheric, to superatrnospheric rangesdepending upon the peculiarities of the given system.

Returning now to FIGURE l, I lhave discovered that solvent extraction`column 1 is effectively operative on typical systems of the `typecontemplated when maintained at atmospheric pressure and within anoperating temperature range of from about 20 to about 150 C., theIpreferred temperature range being `from about 30 to about C.

The yield and purity of the raffinate and extract products, identifiedinfra, from column 1 are, as previously indicated, partially depen-dentupon the number of extraction stages in said column. It is, as a generalrule, true that the greater the num-ber of stages in a solventextraction column, ythe greater will be the yield and purity of theproducts of the column. However, as those skilled in the solventextraction art will appreciate, the selection of an optimum number ofstages is a matter of economics since -as the number is increased apoint of diminishing returns is lreached beyond which the relativelysmall improvement per additional .stage `makes it impractical toproceed. I have found that solvent extraction column =1 is operativelyeffective for use in processes of the contemplated type when it haslfrom about 2 to about l5, and preferably Ifrom 7 to l1, stages.

Referring again to FIGURE 1, an extract phase is withdrawn from thebottom of solven extraction column 1 through line 7 .and a raffinatephase is withdrawn from the top of the column through line 9 as shown.When column 1 is designed and operated according to the preferredprecepts and conditions set forth above, aromatic hydrocarbon yields offrom about to about 99 percent by weight and purities of from about toabout 99 percent by weight are attainable in the extract phase. Theextract phase contains most of the solvent passing through column l, inaddition to that portion of the feedstock which the solvent hasextracted in its travel within the column. The raffinate phase fromcolumn 1, under preferred conditions of operation, typically contains'between `about 90 and about 99.5 percent, by weight, nonaromatichydrocarbons, the remainder being solvent.

In the FIGURE l process, as the drawing shows, there is an alternatechoice of disposition of the raffinate from column l. Thus, theraffinate can be withdrawn from the process through valve 11, with valve13 closed, without further treatment, or it can be circulated todistillation column 17 through line l5, as shown on the drawing, toyeffectuate the recovery of solvent therefrom. Obviously, valve 13 iskept open and valve ll closed in the latter event.

For ease of illustration and simplicity of explanation, the FIGURE lprocess is shown and described in terms of the recovery of all feedstockaromatics in one pass through' column l. However, it is to be understoodthat, as explamed above, my method of solvent extraction is equallyaas-m61 lapplicable to the separation of aromatics into fractionsdiffering as to degree of aromaticit-y, such as for example the recoveryof diaromatics from a feedstock -comprising both diaromatic andmonoaromatic components. To. accomplish this type of separation it isonly necessary -to lassure the proper number of stages in column 1 andthe proper operating conditions to accomplish the purpose. Thedetermination of optimum plate plurality and operating conditions toachieve this, or any other result within thev scope of my invention, isa relatively simple matter to those skilled in the solvent extractionart, 'in the light of the teachings herein, requiring at most a minimumamount of routine experimentation. y

Primarily, the achievement of maximum separating efficacy amongcompounds of varying degrees of aromaticity is a matter of having asufficiently high number of extraction stages -in column 1. In thisrespect, it is pointed out that more stages are required for suchselective extraction, all other things being equal, than for mereseparation of the mixture into aromatic. and nonaromatic fractions.

If it is desired to obtain two or more aromatic fractions from a mixturecontaining both aromatics of differing aromaticities and nonaromatics,the FIGURE 1 process can by relatively simple modification be made toaccommodate this requirement. One way of .accomplishing this is to addone or more additional solvent extraction columns similar to column 1 tothe process, with appropriate lines, fittings and other equipment, Whereneeded, to handle the various streams in the system. For example, if itis desired to separate a diaromatic fraction and `a monoaromaticfraction from a feedstock containing diaromatics, -monoaromatics andnonaromatics, this can vbe done by incorporating an additional solventextraction column in series With column 1; using column 1 to extract thediaromatcs from the feedstock; and utilizing the additional column toseparate the monoaromatics from the nonaromatics in the raffinate phasefrom column 1.

While the FIGURE 1 method is preferably practiced as a continuous orflow process, and that aspect of operation is stressed in thisdescription, it functions equally well as la batch process providedcolumn 1 is 4considered to represent suitable apparatus for batchextraction, countercurrent batch extraction, or the like, purposes.

To continue with the detailed description of FIGURE 1, in the event theraffinate phase fromcolumn 1 is routed to distillation column 17, it isfractionated therein into an overhead product of substantially puresolvent which is passed through line 19 into cooler 21, wherein it iscondensed, and from thence through line 22 to juncture with line 5 andadmixture With the solvent feed to column 1, l

and a bottoms product of nonaromatic raffinate hydrocarbons which iswithdrawn to storage or other disposition through line 18. lOtherappropriate means for separating the raffinate phase into its solventand nonaromatic. fractions, such as, for example, ywater extraction ofthe solvent, can be employed in lieu of the column 1`7 distillationoperation, if desired.

The extract phase from solvent extraction column 1, normally containingfrom about 20 to about 30 percent aromatic hydrocarbons and from about80 to about 70 percent solvent, is passed` through line 7 and intodistillation column 23 wherein it is separated into solvent (overhead)and aromatic hydrocarbon (bottoms) fractions, the former beingrecirculated to solvent extraction column 1 through condenser 24 andline 5, as shown on the drawing, and the latter (bottoms) beingwithdrawn .through line 25. None of the components of the extract phasefrom column 1 decompose at or near their normal boiling points.Furthermore, the boiling points of the extract components are normallyof such magnitude and disposition as to permit distillation of theextract phase at atmospheric pressure and, accordingly, distillationcolumn 23 is preferably operated at about that pressure level. Atatmospheric pressure, the most effective temperature range for operationof column 23 is, in most instances, from about to about 300 C., thepreferred range being from about to about 275 C.

Under certain circumstances, there may be minor quantities ofcontaminating hydrocarbons present in the extract phase from column 1,the exact amounts of such contaminants depending upon, inter alia, theoperating temperatures and pressures of, and the number of stages in,said column. Where such is the case, it is conceivable that thecontaminants will, at le-ast to some extent, accompany the solventoverhead from column 23, possibly in the form lof a minimum boilingazeotrope therewith. While the llikelihood of an occurrence of this typeproducing solvent contamination to any significant extent is remote, itis a relatively simple matter to cure such .an evil by inserting a phaseseparator in line 5 between condenser 24 and column 1 and routing thesolvent phase therefrom t0 column 1. Bottoms product from column 23 isrecovered as the Vfinal extract product from the process or it can becirculated to further treatment, not shown, such as additional solventextraction treatment to break it down into componential aromaticfractions or some form of purification treatment to remove `traces ofsolvent or other contaminant(s) possibly present. Makeup 4solvent isintroduced into the system through line 217 and valve 29 as needed. i vY Turning next to FIGURE 2, it will be noted that the process there issimilar to that -of FIGURE 1 in many respects, differing only in themeans of separating the extract phase into its solvent and aromatichydrocarbon fractions. Thus, in the FIGURE 2 scheme a feed materialcontaining both aromatic and nonaromatic components is introducedthrough line 31 into the bottom of a -continuous countercurrent solventextraction column 33 in which it is subjected to countercurrentextraction by a suitable amine-acid solvent. The solvent is continuouslyfed into the upper portion of solvent extraction column` 33, from asource hereinafter disclosed, .through line 35 as shown on the drawing.The products from column 33 are a raftinate phase which is withdrawnfrom the top of .the column through line 37 and an extract phase whichis withdrawn from the bottom through line 39.

The ranate phase from column 33, lsimilarly to that from solventextraction column 1 of FIGURE l, is subject to an alternate choice ofdisposition. either withdrawn through valve 4,1, with valve 43 closed,to storage or with destination not shown or it is routed to distillationcolumn 47 through line 45 by proper manipulation of valves 41 and 43,wherein it is factionally distilled to separate it into an overheadsolvent product and a bottoms product of nonaromatic rainatehydrocarbons which is withdrawn through line 49. It should be undertsoodthat the various alternatives as to technique, apparatus, feedmaterials, etc., set forth in the description of the FIGURE 1 processhave equal significance with respect to those elements of the FIGURE 2process which are common to both methods of operation.

The solvent overhead from distillation column 47 is routed through line51 into cooler 53, wherein it is condensed, and from thence through line55 to juncture with line 35 and admixture with the solvent being'fed tocolumn 33. f

The extract phase from solvent extraction column 33 is` passed intosolvent extraction column S7, throughl line 39, wherein the solvent(being Water soluble, as pointed out infra) is selectively extractedtherefrom with Water. The extraction of the slovent from the extractphase is not limited to the use of waterl asthe extracting agent and anyother material which is a relatively stable liquid under the conditionsof service, and in which the amine-acid solvent is substantiallymiscible, may be employed for the purpose if desired. It is, of course,obvious that the chosen material must also be substantially immisciblewith the hydrocarbon, or hydrocarbons, in the extract f phase.

Thus, it is The products from column 57 are an aqueous solution of theamine-acid solvent (aqueous phase) which is withdrawn from the bottom ofthe column through line 59, and a hydrocarbon product consisting of thearomatic fraction of the feedstock in substantially pure form, which iswithdrawn through line 61 to storage or other disposition.

The aqueous solution of solvent from column 57 is passed through line 59to a distillation column 63 in which the Water is separated from thesolvent, the water passing ot through line 65 as an overhead and thesolvent being withdrawn through line 3S as a bottoms product. The wateroverhead from column d is condensed in condenser 69 and thenrecirculate-d to solvent extraction column 57 through line 71 as shownon the drawing. The solvent bottoms product from column 63 is recycledthrough line 35 to solvent extraction column 33.

Column 57 is shown schematically as a countercurrent solvent extractioncolumn and the preferred technique for practicing the FIGURE 2 processis by continuous operation of that unit, as well as all other units inthe process. However, it is possible to replace `column 57 by batchapparatus for solvent extraction if desired. It is also possible tomodify the FGURE 2 process in other ways obvious to those skilled in theart without substantial alteration of its purpose or accomplishments.One such modification is, for example, the incorporation of knownpurication techniques for the treatment of one or more of the productsof separation from solvent extraction column 57, as well as distillationcolumn 63. Makeup solvent is introduced into the FEGURE 2 processthrough line 67 and valve 73 as needed.

There are a number of things to consider in the selection of solventsfor solvent extraction purposes, among which are: (l) the stability ofthe candidate material under the conditions (heat, pressure, etc.) ofservice; (2) the selectivity of said material, under service conditions,with respect to the mixture to be extracted; (3) the tendency or lack ofsuch tendency of the material to react chemically with any of thecomponents of systems in which it will be used; (4) its boiling pointrelative to the boiling points of the `components of the mixtures to beseparated; (5) its melting point; (6) its corrosiveness t0- wards thematerials of construction of the equipment to be employed; (7) itstoxicity (which is important from an operational standpoint); (8) itswater solubility; and (9) its density relative to the densities of thecomponents of the mixtures to be separated. I have now discovered thatmixtures of amines and acids varying widely as to ingredient compositionand component proportions satisfy all of the requirements inherent inthe above considerations to qualify as excellent solvents for theselective extraction of aromatic hydrocarbons from organic mixtures ofthe type previously disclosed. I have further found that, in addition tohaving an ainity or selectivity for aromatic hydrocarbons in general,such amine-acid mixtures have relatively greater selectivities foraromatics of relatively greater degrees of aromaticity, thus making theseparation of aromatics by degree, as discussed in detail supra,possible by solvent extraction means.

The amine-acid mixtures suitable as selective solvents for use in myinvention must, of necessity, be liquid under the service conditions ofmy solvent extraction method. I have determined that best results areusually achieved when molar ratios of acid to amine within the rangefrom about 1:1 to about 6:1 (optimum: from about 2:1 to about 4:1) areemployed. It is of interest to note that amines and acids often formmaximum boiling azeotropes and, in this connection, I have made theinteresting discovery that the preferred acidzamine ratios for purposesof this invention typically correspond to maximum boiling azeotropecompositions.

The amines of most effectiveness for use as taught herein are tertiaryamines having from about 3 to about 15, and preferably from about 3 toabout 9, molecular carbon atoms. The amines may be wholly orpredominantly of aromatic, aliphatic or heterocyclic character, or theymay partake, in varying degrees, of the characteristics of compounds inany two, or all three, of those categories. Amines which are otherwisesuitable having substituent groups of a substantially neutral characterwith respect to other components in the system can be employed for mypurpose if desired.

The amine-acid solvents of this invention are not amides but merelymixtures of amines and acids. Such mixtures are sometimes referred to assalts. However, the term salts has been deliberately avoided herein toobviate any possibility of misunderstanding as to its meaning.Furthermore, the amine and acid ingredients are not always present in mysolvent mixtures in amounts stoichiometrically consistent with saltproportions so the term salts would not be precisely applicable in thosecases anyway. Since my class of amine-acid solvents is exclusive ofamides, it will be apparent that combinations ot amines and acids whichreact to form such compounds under the conditions encountered in thepractice of my invention are outside of the scope of said invention.Secondary and primary amines generally react with organic acids to yieldamides whereas tertiary amines do not so react with those acids. As willbe presently made clear, the aci-d ingredients of my amine-acid solventsare organic acids. Hence, only tertiary amines, and not secondary orprimary ones, are normally suitable for use as the amine ingredients ofmy solvent mixtures.

The following tertiary amines are representative of those amines mostsuitable for use in this invention:

Triethyiamine Triphenylarnine Trimethylamine DimethylanilineMethyldibutylamine Methyldiphcnylamine Dimethylbutylaminel-methylpyrrole Ethylmethylpropylamine EthyldipropylamincDiethyloctylamine Diethlypropylamine N,N-dimethylpiperazine1,3-dirnethylpyrrole l-dimethyiamino-3-butene ot-Picoline 3 ,S-lutidine2,4,6-collidine N-ethylpiperidine MethylethylisobutylamineTriethylenediamine N- l -ethylbutylidine-ptoluidine Any organic acidyielding a liquid mixture under service conditions within the reach ofthis invention when combined with Ian amine, or amines, of proper typeis a suitable acid ingredient for my amine-acid solvent. The organicacid can be of any type, such as, for example, an alkanoic, benzoic,etc. acid, and it can be nnsubstituted or substituted. Examples ofrepresentative acids are monocarboxylic acids such as formic, acetic,propionic, etc., acids; substituted monocarboxylic acids such astriiiuoroacetic, rnonochloroacetic, diehloroacetic, trichloroacetic,a-bromocaprioic, etc. acids; sulfonic acids such as ethylsulfonic acid,butylsulfonic acid, etc.; unsaturated acids such as acrylic acid, oleicacid, etc.; substituted unsaturated acids such as ,-dibromopropionicacid, etc., hydroxy acids such as glycolic acid, lactic acid, etc.;aldehydic acids s uch as glyoxalic acid, etc.; ketonic acids such asketoproplonic acid, etc.; amino acids such as lysine, ornithine, etc.;aromatic aminobenzoic acids such as oaminobenzoic acid, etc.; aromaticsubstituted and unsubstituted acids such as benzoic acid, o-phthalicacid, phenylacetic acid, cinnamic acid, p-nitrobenzoic acid, o-toluicacid, m-toluic acid, p-toluic aci-d, ni-bromobenzoic acid,

p-chlorobenzoic acid, o-sulfobenzoicacid, salicylic acid, gallic acid,mandelic acid, cinnamic acid, etc., alicyclic acids such ascyclopentano-l,2dicarboxylic acid, truxillic acid, truxinic acid, etc.;and heterocyclic acids such as furoic acid, furylacrylic acid, nicotinicacid, barbituric acid, tryptophane, indol--acetic acid, quinolinic acid,cinchophen, 2-phenoxybenzoic acid, tnt-pyridine carboxylic acid, etc.

The method of preparing the amine-acid mixtures lfor use as solvents inthis invention is simple, it being only necessary, in most instances, toadd the amine to the acid, or vice versa, in the desired amount,normally'such an amount as to yield a final mixture containingazeotr'opic proportions of the two materials where such proportions arepossible. y

My invention is not limitedto the use of amine-acid mixtures ofazeotropic proportions and other mixtures can be employed if desired.Examples of `such other mixtures are those combinations of azeotropeforming amines and acids in nona'z'eo'tropic proportions andcombinations of nonazeotrope forming amines and acids.

The use of mixtures of two or more amines and/or acids, instead of onlyone lamine and one acid, is within the scope of my invention. AS`indicated previously, the amine-acid solvent must be in liquid formunder the conditions of service of my solvent extraction method. Thisdoes not mean that the amine acid mixture must be liquid at standardconditions of room temperature and atmospheric pressure, although suchis frequently the case. It is within the scope of the invention toemploy amines and/ or acids which are solid at standard conditions, orform solid or semi-solid mixtures thereat, so long as the resultingamine-acid mixtures are liquid under the operating conditions to beemployed in the solvent extraction systems in which they are to be used.v

In the preparation of solvent mixtures according to this invention, ifthe ingredients are all liquid at room temperature, simple stirring isusually sufficient to effect rapid homogeneity of the mix. Where not allof the ingredients are liquid at the temperature of preparation, itmight be necessary to use more rigorous means of achieving uniformity ofmix such as, for example, kneading or the like. In either event, theapplication of heat to change the viscosity characteristics of thesystem can be employed if desired.

The preferred solvents for my solvent extractionprocess are thosemixtures`of trialkylamines, such as triethylamine, and lower alkanoicacids havingv carbon chain lengths not greater than about 6, such asacetic acid, etc., in which the amine and acid components are present-in their azeotropic proportions.` These mixtures form maximum boilingazeotropes and I have determined that mixtures corresponding incomponent proportions to such azeotropes are highly selective towardaromatics for purposes of this invention. In addition, the boilingpoints of these particular mixtures are sufficiently low to permitrelatively easy and inexpensive separation of the solvents from theirhydrocarbon mixtures by distillation. In addition, the components ofthese preferred mixtures are 'cheap and readily available. Otheramine-acid mixtures worthy of note as outstanding .solvents for use inthe present invention are prepared by mixing an l -alkylpyrrolidine,such as N-methylor N-ethylpyrrolidine, with a lower alkanoic acid, suchas acetic acid, in az'e'otropic proportions. These mixtures are highlyselective solvents for aromatic hydrocarbons and in addition, arepossessed of relatively high densities which, as those skilled in theart realize, is highly advantageous in a selective solvent.

It should be emphasized that even though molar excesses of acids arenormally used in the preparation of my selective solvents, thecorrosivity of the solvents to ward materials vulnerable to acid attackis unexpectedly low, sometimes approaching that of distilled water. Thisis obviously of major importance from the standpoint of equipmentecono-my and simplicity of maintenance. The reason for the surprisinglack, or minimization, of corrosivity in my selective `solvents is notunderstood with certainty. Y

The solvents of this invention, in addition to Ibeing highly selectivetoward aromatic hydrocarbons, exhibit high solvent power, i.e.,relatively small quantities of solvent dissolve relatively largequantities of .aromatics More specifically, solvent proportions of fromabout 0.25 to about 3.0l parts of solvent' (my preferred proportions) toabout l part of hydrocarbon feedstock, on a weight basis will normallymanifest a solvent power of from about 5 to about 35. The method ofcalculating solvent power values forpurposes of this invention is setforth in Example II following.

An important factor in arriving at optimum conditions of operation insolvent extraction processes is the rapidity with which the raffinatephase separates from the extract phase under various circumstances. Byusing the preferred tertiary amine-acid solvents in the method of myinvention, relatively rapid separation takes place between the phaseswhen operating at room temperature. At higher temperatures, phaseseparation is faster and the solvent power of the amine-acid solvent isgreater, but temperature increases have an adverse effect on theselectivity of the solvent towards aromatics. The previously recommendedtemperature ranges for the practice of my invention (about 20 to about150 C., preferably from about 30 to about 60 C.) were arrived at bytaking the aforesaid factors into consideration. The relatively fastphase separation achievable with my .amineacid solvents is thought to beattributable, at least in part, to the fact that they have highdensities, normally in excess of one, compared to hydrocarbon oils.

The solvents of this invention are relatively nontoxic at standard, aswell as operating, conditions. Also, these solvents are miscible withwater, thus making it an easy matter to recover them from extractphases, by water extraction, for recycling or oit-her purpose. Inaddition, the solvents are stable at their boiling points and unreactivewith the feedstock components at those temperatures, as well as othertemperatures to which they are subjected in service. The preferredtertiary amine-acid azeotropic mixtures of this invention have boilingpoints ranging between about and about 300 C. Those having boilingpoints within the range from about to about 275 C. have been found mostefficacious for use in my process.

The solvent extraction process of my invention can lne carried out invarious ways, the most common mode of operation comprising the use of aspray, packed, or bubble plate tower, wherein the hydrocarbon feedmixture is contacted by the stream vof amine-acid solvent iiowing,usually countercurrently, therethrough. It is within the scope of myinvention to .add a minor amount of water, or other inert agent, to myamine-acid solvents, where such can .be done with colorable modificationof those solvent properties necessary to the proper functioning of myprocess. -F or example, where it is proposed to subject a mixture ofhydrocarbons of varying degrees of aromaticity to solvent extractionaccording to my method, and the hydrocarbons are all quite soluble inthe lchosen solvent, the incorporation of a minor amount of water intothe solvent, prior to or during the extraction operation, to assure therapid and distinct formation of two liquid phases is within the spiritand scope of my invention. When water is added for such purpose, theproportion used should normally not exceed about 20 percent of theweight of the solvent and preferably fall within the range from about 2to about 5 percent of the solvent weight.

If desired, my process can be carried out by distilling the hydrocarbonfeed mixture in the presence of an 1 1l amine-acid solvent, of the typedisclosed herein, as an extractive distillation process.

In the practice of extractive distillation, a feed mixture to beseparated is -distilled in the presence of a selective solvent which hasa substantially lower volatility than any of the components of saidmixture as a result of which an overhead enriched in that portion of thefeed mixture not selectively extracted is removed, leaving behind abottoms product which comprises a solution of solvent and selectivelyextracted materia-l. Since not all of my amine-acid solvents are oflower volatility than all components of those feed mixtures separable bymethods taught herein, it is necessary to .be selective in choosing asolvent of proper volatility for the extractive distillation of a givenfeedstock in accordance with this invention. To illustratean amine-acidsolvent suitable for the extractive distillation of a petroleum fractionhaving a boiling range of from about 400 to about 450 F., such as aheavy refer-mate fraction containing naphthalene, alkyl naphthalenes,alkyl benzenes, tetralins, indanes, etc., must lboil at a temperaturelevel much higher than 450 F. Examples of solvents fitting this categoryare mixtures of tributylarnine and caproic acid, mixtures ofdimethylaniline and benzoic acid, etc.

Still another way in which my process can be carried out is to employ anatisolvent in conjunction with the amine-acid solvent in any mannerknown to `those skilled in the art. The use of such antisolvents inhydrocarbon solvent extraction processes is `well known and need not beconsidered in detail here. Typical antisolvents for purposes of thisinvention are paraflins such as pentane, heptane, octane, isooctane, andthe like; water; etc.

In order to more fully illustrate the invention lthe folcarbons and76.5% by weight solvent, and a rainate phase containing 99.3% by weighthydrocarbons and 0.7% by weight solvent were produced. The solventfreeextract was about 73.5% by weight naphthalenes, and the solvent-freeraffinate was about 15% by weight naph- -thalenes The solvent wasremoved from the extract phase, by fractional distillation, whichyielded a bottoms product containing 86% by weight naphthalenes. Theoverall recovery of naphthalenes from the feed was 78%.

This example serves to illustrate the selectivity of my preferredtertiary amine-acid mix-tures as solvents for diaromatics in th-epresence of monoaromatics, as well as the relatively high solvent powerof such mixtures towards diaromatics. The use of additional stages inthe method of this example results in a substantial increase in extractpurity and yield of diaromatics. Thus, recoveries of from about to about99 percent of the naphthalencs in the feed stock and extract productpurities of from about to about 99 percent diaromatics are attained bythe use of such additional stages.

EXAMPLE II A number of one-stage tests were conducted using as selectivesolvents various tertiary amine-acetic acid mixtures. Thehydrocarbon-solvent batch was prepared by adrnixing 10 ml. of solvent,10 ml. of decalin and 5 ml. of ic-methylnaphthalene. Thea-methylnaphthalene and decalin represent the feedstock.a-Methylnaphthalene was separated by the solvent as the extract phase.Decalin is a bicyclic paraflin. All solvent mixtures were prepared inazeotropic component proportions. The results appear in Table I,following:

Table I TERTIARY AMINE-ACETIC ACID AZEOTROPES FOR AROMATICS PURIFICATIONWeight Percent Percent 13.1. Amine B.P. Percent D 25 C. Naph. PurityAmine, Stability Solvent 1 C.) HAc 1n Recovery 0f Naph C. PowerAzeotrope N-cthylpyrrolidiue 170 64 1. 023 47 67. 8 106 Good 16, 2Triethylamine 163 68 1. 003 44 68. 1 90 Very gooCL.. 15. 4N-methylpyrr0lidine 168 76 1. 047 34 69. 8 83 Good 12. 4Methyldibutylamine 161 65. 5 9874 42. 5 60. 0 11. 4 N-methylpipcridine165 68 l. 047 30 71. 5 11, 5 N,N,N/,N'-tetramethylethyl- 171 64 l. 03933 67. 8 1l. 4

enediamine.

N,N-dimethylethanolaminc 162 62 1. 062 26 73. 1 10. 4 N-methylmorpholine152 66 1. 081 27 71. 0 10. 2 N,N'dimetliylpiperazine 168 62 1. 052 3661. 0 10, 0 Trimethylamine 152 80 1. 035 24 72. 0 9, 3 Pyridine 14153 1. 039 25 66. 0 S, 2

l Diierence in a-methylnaphthalenc concentration between thesolvent-free extract and the feedstock times percent recovery times 10-2. lowing examples are set forth. These examples are to be consideredas illustrative only and not limitative of the scope of the invention.

EXAMPLE I Using 100 gms. (100 ml.) triethylamine-acetic acid solvent, asimulated continuous solvent extraction in three stages was carried outat atmospheric pressure using 75 gms. (83 ml.) of catalytic cycle oil asfeed. Approximately 68% by weight of the solvent was acetic acid and theweight ratio of solvent to feed was 1.33 to 1. The feed was ahydrocarbon fraction which boiled at a range between 445 F. and 500 F. Ahydrocarbon type analysis showed the following approximate composition(weight percent):

Parains 17 Naphthenes 2l Monoaromatics 20 Diaromatics 1 42 1 Consisting'of methylnaphthalenes (14 percent on n total feed Weight basis) anddimethylnaphthalenes (2S percent on a total feed Weight basis).

An extract phase containing 23.5% by weight hydro- Table I provides muchvaluable information.

The boiling point of the solvent is higher than the boiling point ofeach of its components considered separately. For instance, the boilingpoint of acetic acid is about 118 C. The boiling point ofN-ethylpyrrolidine is 106 C. (column 6) but the boiling point of thesolvent is C. which indicates that the solvent is a maximum boilingazeotrope. This boiling point is sufficiently lower than that ofa-methylnaphthalene (244.6 C.) to permit substantially completeseparation of high purity solvent from the solvent extraction extractphase by fractional distillation.

Column 2 of Table I indicates the percentage of acid in the solvent. Inspite of the high percentages of acid in every case, the corrosivity ofthe solvent was generally low-in some cases not significantly greaterthan that of distilled water. v

With one exception (methyldibutylamine), the solvents had a densitygreater than one, thereby indicating ease of separation between theextract and raffinate phase. Even in the case of the exception(methyldibutylarnine), the density was sufficiently higher than that ofthe feedstock to assure good phase separation. In this connection, it isi previously indicated, substantial increases in yield and purity.,Examplel oiers'. evidence ofthis in the'f'act that a `yield of 78% anda purit'yo'f 73.5% was obtained in threustages. Still more stageswould,as'pointed` outpreviously, result in yieldsV and purities representingalmost ideal separation of the feed components.

Column 7 gives an indication of the stability vof the liste-d solventsat their boiling points. As column 7 shows, onlythe N,Ndiethanolamineresulted in a -solvent having poorboiling point stability. However, eventhough that solvent is not particularly stable at .its boiling point, itis a good solvent as evidenced by the .data of columns 4 land 5. It alsohas -a relatively high boiling point (maxim-um boiling azeotrope). Inview of these facts, the relatively poor boiling .pointV stability .ofthe ance being composed of Arnonoaromatics 4such as those named above.Thus, it can be determined that the ratio of diaromatics tomonoarornatics increased from 1.73 in the feed lto 3.67 in the extract.

Theabove results clearly show that there was greater selectivity ofthe*solvent for the diaromatics than for the'mon'oaromatics present in thesystem.

.EXAMPLE ,IV

This exampleillustrates the utility of various amine- 'acid combinationsas selective solvents for diaromatics in the presence. ofmonoaromatics.

' A-hydrocarbon dealkylation product containing 40% naphthalene and 60%alkylatedmonoa-romatics and nonaromatics such as naphthenes, alkylindanes, alkyl indenes, alkyl .tetralins, and the like, ,was dividedinto g. samples. Each sample was `mixed with 4125 g. of a separatesolvent fro-m thelist in Table II, below. A single stage solventextraction process for each sample was then carried out at a temperatureof 125 C. The results are tabulated in Table II, following.

Table I I Percent Purity of Percent Compound B .1. Diaro- Exact Acid inSolvent Density 1 C.) matics (Percent) Azeotrope Power Recovery'rriethyimme-fomn Acid Azeotrope 18e 35. 5' s4. 1 e7. 0 1s. 2 1. 0179Triethylamine-triiluoro-acetic 'Acid Azeotrope 235 4G. 5 76. 8 59. 5 20.2 1. 1916 Triethylamine-methoxy-acetic Acid Aze- Otlope 2 18 33. 8 79. 080. 0 l5. 4 yl. 0743 Diethylcyclohexylarnine-aceticAcidAzeotrope 175 59.5 55. O 55. 0 12. 9 9789 Nora-All percentages in the above table are ona weight basis.

solvent does not r-ule out its use as a selective solvent for my new-process and there are techniques known to those skilled in the art forrecovering the `solvent from ythe extract phase without subjecting'it totemperatur-es 'potentially damaging to its stability. For example, the

extract lphase can be fractionally distilled at reduced pressures topenmit operation at lower temperatures lor it can'be extracted withwater to selectively dissolve out the solvent in accordance with the`FIGURE 2 pro- This example illustrates the selectivity of my amineacidsolvents Vfor diaromatic hydrocarbons in the presence o-fmonoaromati-chydrocarbons.

A 133 ml. lquantity of N-methylpyrrolidine and acetic acid was ad-mixedwith 100 ml.` of a hydrocarbonfraction having aboiling range of 430-520F. The acetic acid comprised 76% by weight of the solvent and the weightratio of `solvent toy feed was 1.33 to 1.` The hydrocarbon fractionwascompo-sed of 58.3% monoaromatics and diaromatics, including naphthalene,methyland dimethylnaphthal'enes, Valkyl indanes, alkyl indenes,alkyltetralins, and thel like The balance of the hydrocarbon fraction(41.7%) was composed of parans and naphthenes. The ratio of di'aromaticsto monoaromatics in the hydrocarbon fraction was 1.73 to 1.

The mixture of solvent and hydrocarbon fraction .was moderately agitatedat '25 C. and allowed to settle into a rainate and extract phase. Theextract phase after analysis showed an aromatic concentration of 95.2%which was found to be 74.3% diaromati-cs such as naphthalene, andmethyland dimethylnaphthalenes, theV balvof this invention.

The rirst two solvents listed in Table II have maximum boiling azeotropecompositions which are unstable at their boiling points. However, hereagain, as in the case of the N,N-dimethylethanolamine-acetic acidsolvent of Example II, and Vfor the same reasons, .the solvents are notthereby rendered ineligi-ble for use in my invention. i

Columns 2 and 3 of Table II list naphtlralene recovery and purityresults. It is to be noted that even though the first two listedsolvents in Table II decompose at their boiling points they areextremely effective solvents, the recoveries and purities, andparticularly the latter,

,attributable to their use being exceptionally high for a one-stageoperation.

Column `5 sets forth the solvent powers of the solvents which, it willbe observed, `are relatively high, indicating good perfor-mancecapability in the solvents for purposes The superiority in solvent poweris accented by the rather low ratio of solvent to feed employed in thedescribed procedure.

EXAMPLE V This was an example of a laboratory-scale solvent extractionof rnethylnaphthalene from a mixture of niethylnaphthalene (adiaromatic) and dodecane (a paraffin), using a mixture of triethylamineandv acetic acid as the solvent.

A single stage solvent extraction was carried out at 25 C. by treating amixture of 14 ml. of dodecane and 6 ml. of methylnaphthalene with 16rnl. of triethylamineacetic acid solvent. v The weight ratio of solventto hydrocarbon feed mixture was approximately 0.8 to 1. Approximately68% of the solvent was acetic acid. The .solventhydrocarbon mass wasmoderately agitated and a solvent rich phase separated therefrom.. Itwas determined that approximately 21% of the volume of the This exampleillustrates the selective extraction of diaromatics from a mixturethereof with monoaromatics according to the method of this invention.

100 grams (100 ml.) of a triethylamine-acetic acid mixture at C. isadmixed with 75 g. (83 ml.) of a hydrocarbon fraction composed 60% ofdimethyltetralins and dimethylnaphthalenes. 68% of the solvent comprisesacetic acid and the ratio of solvent Ito hydrocarbon fraction is 1.33to 1. A two-phase separation is conducted in which the diaromatics areabsorbed in the solvent rich phase.

The solvent rich or extract phase contains about 20% diaromatichydrocarbons and about V80% solvent and monoaromatic hydrocarbons. Therecovery, or yield, of

diaromatic hydrocarbons effected bythe method de-`" scribed in thisexample is equal to An increase in the number of stages increases theyield and purity of the extract product to between 85-99% and 90-99%,respectively.

i EXAMPLE VII This example illustrates the selective extraction ofmonoaromatic hydrocarbons from a mixture thereof with nonaromatichydrocarbons according to the method of this invention.

100 grams (100 ml.) of a mixture of 68% acetic acid and 32%triethylamine is admixed at 25 C. with a hydrocarbon fraction composedof 20% benzene, toluene and xylene and 80% parathns and naphthenes as aresult of which an extract phase rich in the monoaromatic hydrocarbonsis recovered. The extract phase is composed of about 20% monoaromatichydrocarbons and 80% solvent and nonaromatic hydrocarbons and containsabout 47% of the monoaromatic hydrocarbon content of the feedstockmixture.

Here, as in the case of the other examples, the yield and purity of theextract product is greatly increased by an increase in the number ofsolvent extraction stages.

EXAMPLE VIII The following example illustrates the use of' a solventcontaining a minor amount of .water in the process of my invention.

A selective solvent composed of 32 parts triethylamine, 5 parts water,and 68 parts acetic acid was prepared. 10 ml. of the solvent was admixedwith l0 ml. of decalin and 5 ml. of methylnaphthalene and the resultingbatch was agitated and allowed to separate into an extract phase and aratiinate phase. The extract phase was analyzed for itsmethylnaphthalene content and it was found to contain 27% of themethylnaphthaleneV origi-l nally introduced and to have a purity,solvent-free, of`

The solvent had a density of 1.003 and lboiled at 100- 163 C., the 100C. being the boiling point of the Water therein.

The solvent was found to be stable over its boiling point rangemaking'fractional distillation of the extract phase to separate solventfrom the aromatic hydrocarbon feasible.

EXAMPLE IX This example illustrates the use of atriethylamineethylsulfonic acid mixture as a solvent in the method ofmethylnaphthalene in the amount of 33 percent by weight, is treated withg. of a triethylamine-ethanesulfonic acid mixture (47.6 percent byweight triethylamine and 52.4 percent by weight ethanesulfonic acid) ina onestage solvent extraction process.

The extract phase from the solvent extraction process is subjected to awater extraction treatment whereby its triethylamine-ethylsulfonic acidsolvent portion is selectively extracted by the water. The remaininghydrocarbon portion is enriched in methylnaphthalene.

EXAMPLE X This is an example of the use of an antisolvent in thepractice of my invention.

A single stage solvent extraction operation is carried out at 25 C. bytreating a mixture of 14 ml. of dodecane and 6 ml. of methylnaphthalenewith 16 ml. of triethylamine-acetic acid solvent (approximately 68percent acetic acid) at a weight ratio of solvent to hydrocarbon feedmixture of approximately 0.8 to 1. The solventhydrocarbon mixture ismoderately agitated and a solventrich extract phase is separatedtherefrom.

V.Thesolvent-richextract phase is Washed'with pentane, as anantisolvent, to selectively extract dodecane which is dissolved thereinas a contaminant. As a result of the washing operation, two phases (apentane rich phase containing dodecane and a solvent-rich phasecontaining methylnaphthalene) are formed. The two phases areseparated'and the solvent-rich phase is distilled to remove thetriethylamine-acetic acid solvent as an overhead and recover themethylnaphthalene as a bottoms product.

EXAMPLE XI This example illustrates the use of a tributylaminecaproicacid mixture as a solvent in the method of my invention.

A l0() g. hydrocarbon feed sample comprising paraffins, naphthenes,alkyl indanes, alkyl indenes and alkyl tetralins, in the amount of 67percent by weight, and methylnaphthalene in the amount of 33 percent byweight is treated with 100 g. of a tributylamine-caproic acid mixture(40 percent by weight tributylamine and 60 perment by weight caproicacid) in a one-stage solvent extraction process. The solvent-hydrocarbonfeed mixlture is moderately agitated and a solvent-rich extract phase isseparated therefrom.

Thesolvent-rich extract phase is separated by distillation into asolvent fraction and a hydrocarbon extract product rich inmethylnaphthalene.

EXAMPLE XII This example illustrates the use of a dimethylanilinebenzoicacid mixture as a solvent in the method of my invention. y

A 100 g. hydrocarbon feed sample comprising paraftins, naphthenes, alkylindanes, alkyl indenes and alkyl tetralins, in the amount of 67 percentby weight, and methylnaphthalene in the amount of 33 percent by Weightis treated with 100 g. of a dimethylaniline-benzoic acid mixture (35percent by weight dimethylaniline and 65 percent by weight benzoicacid)A in a one-stage solvent extraction. The` solvent-hydrocarbon feedmixtureis 'Amoderately agitated and a solvent-rich extract phase isseparated therefrom.

Thesolvent-rich extract phase is separated by distillation into asolvent fraction andahydrocarbon extract product rich inmethylnaphthalene. v

K EXAMPLE XIII This example illustrates the use of atropane-triuoroacetic acidmixture as a solvent in the method of myinvention. v f Y. K l

A 100 g. hydrocarbon feed sample comprising parafiins,

naphthenes, alkyl indanes, alkyl indenes and alkyl tetralins, in theamount of 67% by weight, and methylnaphthalene inthe' amountof 33% byweight is treated 17 with 100 g. of a tropanetriliuoro-a'oetic acidmixture (.30 percent by weight tropane and 70 percent by weighttrifluoro acetic acid) in a one-stage solvent extraction process. Thesolvent-hydrocarbon feed mixture is moderately agitated and asolvent-rich extract phase is separated therefrom.

The solvent-rich extract -phase is separated by distillation into asolvent fraction and a hydrocarbon extract product rich inmethylnaphthalene.

It will be apparent that many modifications of my process can bepracticed simply by varying the permissible solvent components, feedmaterials and 'operating techniques Within the limits taught herein. Allpercentage data in the above examples and elsewhere in this 'disclosureare on a weight basis unless otherwise specified.

The present process is particularly well adapted to preparing feedstocksfor dealkylation processes. Thus, a heavy reformate fraction containingalkyl naphthalenes and non-naphthalenic materials can be treated inaccordance with the invention to obtain an alkylnaphthalene concentratewhich is thereafter dealkylated to form naphthalene by .any of theconventional catalytic or thermal dealkylation processes.

I claim:

1. A method of separating hydrocarbon material of greater aromaticityfrom a mixture thereof with hydrocarbon material of lesser aromaticitywhich comprises contacting said mixture with a substantially amide freesolvent comprising a mixture of a tertiary amine and an organic acidselected from the group consisting of carboxylic and sulfonic acids.

2. A method of separating hydrocarbon material of greater aromaticityfrom a mixture thereof with hydrocarbon material of lesser aromaticitybut roughly the same boiling point which comprises subjecting saidmixture to extractive distillation in the Vpresence of a substantiallyamide free solvent comprising a mixture of a tertiary amine and anorganic acid selected from the group consisting of :carboxylic andsulfonic acids.

3. A method of extracting hydrocarbon material of greater aromaticityfrom a mixture thereof with hydrocarbon material of lesser aromaticitywhich comprises contacting said mixture with a solvent comprising amixture of a tertiary amine and an organic acid selected from the groupconsisting of carboxylic and sulfonic acids to form an extract phaselcontaining hydrocarbon material rich in said hydrocarbon material ofgreater aromaticity, and a raffinate phase. v 4. A method of extractinghydrocarbon material of greater aromaticity from a mixture thereof withhydrocarbon material of lesser aromaticity which comprises: (1)contacting said mixture with a solvent comprising a mixture of atertiary amine and an organic acid selected from the group consisting ofcarboxylic and sulfonic acids to form an extract phase containinghydrocarbon material rich in said hydrocarbon material of greateraromaticity, and a raffinate phase and (2) recovering substantially allof the hydrocarbon material of greater aromaticity from said extractphase.

5. The method of claim 4 in which the hydrocarbon material of greateraromaticity is recovered from the extract lphase by fractionaldistillation means.

6. A method of extracting hydrocarbon material'of greater aromaticityfrom a mixture thereof with hydrocarbon material of lesser aromaticitywhich compris-es: (1) contacting said mixture with a solvent comprisinga mixture of a tertiary amine and an organic acid selected from thegroup consisting of carboxylic and sulfonic acids to form an extractphase containing hydrocarbon material rich in said hydrocarbon materialof greater aromaticity but containing a minor amount of said hydrocarbonmaterial of lesser aromaticity, and a raiiinate phase; (2) treating theextract phase with an antisolvent to extract said hydrocarbon materialof lesser aromaticity 18 therefrom; and (3) recovering substantially allof the hydrocarbon material of greater aromaticity from the thus treatedextract phase.

7. A method of extracting diaromatic hydrocarbons from a feedstockcontaining diaromatic, monoaromatic and non-aromatic hydrocarbonscomprising: (1) continuously contacting said feedstock, incountercurrent relationship, with a solvent consisting essentially of amixture of a lower alkanoic acid and a trialkylamine at a molar ratio ofthe former to the `latter of from about 1:1 to about 6: 1, whereby anextract phase rich in said solvent and containing a portion of thefeedstock enriched in diaromatic hydrocarbons and a raiiinate phasecontaining substantially all of the remaining portion of the feedstockand a minor amount of said solvent, are obtained; (2) subjecting theextract phase from step (l) to fractional distillation to form anoverhead product of substantially pure solvent and a hydrocarbon bottomsproduct enriched in diaromatic hydrocanbons; 3) condensing the overheadsolvent product from step (2); and (4) recycling the condensed solventfrom step (3) to step (l).

8. A method of extracting diaromatic hydrocarbons from a feedstockcontaining diaromatic, monoaromatic and nonaromatic hydrocarbonscomprising: (l) extractively distilling said feedstock in the presenceof an extractive distillation solvent consisting essentially'of amixture of a lower alkanoic acid and a trialkylamine at a molar ratio ofthe former to the latter of from about 1:1 to about 6:1, whereby anoverhead fraction of the feedstock enriched in monoaromatic andnonaromatic hydrocarbons and a bottoms product containing said solventand a portion of the hydrocarbon feedstock enriched in said diaromatichydrocarbons, are obtained; (2) subjecting the bottoms product from step(l) to fractional distillation to form an overhead product ofsubstantially pure solvent and a hydrocarbon bottoms product enriched indiaromatic hydrocarbons; (3) condensing the overhead solvent productfrom step (2); and (4) recycling the condensed solvent from step (3) tostep (l).

'9. The method of claim 7 in which the trialkylamine is tricthylamineand the lower alkanoic acid is acetic acid.

10. The method of claim 7 in which step (1) is conducted at atmosphericpressure and at a temperature within the range from about 20 to about150 C.

11. The method of claim 7 in which the ratio of solvent to hydrocarbonfeedstock in step (l) is from about 0.25 to about 3.0 parts by weight ofthe former to l part by weight of the latter.

12. The method of extracting diaromatic hydrocarbons from a feedstockcontaining diaromatic, monoaromatic and non-aromatic hydrocarbonscomprising: (1) continuously contacting said feedstock, inlcountercurrent relationship, with a solvent consisting essentially of amixture of a lofwer alkanoic acid and a trialkylamine at a molar ratioof the former to the latter of from about 1:1 to about 6:1, whereby anextract phase rich in said solvent and containing a portion of thefeedstock enriched in diaromatic hydrocarbons and a raflinate phasecontaining substantially all of the remaining portion of the feedstockand a minor amount of said solvent, are obtained; (2) subjecting theextract phase Vfrom step (l) to water extraction to form an aqueousphase containing substantially all of the water from the waterextraction step and substantially all of the solvent in said extractphase and a hydrocarbon phase containing substantially all of thediaromatic hydrocarbons from said extract phase; (3) subjecting theaqueous phase from step (2) to fractional distillation to form anoverhead product of substantially pure water and a bottoms product ofsubstantially pure solvent; (4) recycling the solvent bottoms productfrom step (3) to solvent extraction step (1); (5) condensing theoverhead water produ-ct from step (3); and (6) recycling the condensedwater from step (5) to water extraction step (3 13. The method of claim-12 in which the trialkylamine is triethylamine and the lower alkanoicacid is acetic acid.

14. The method of claim 12 in which the raflinate phase from step (1) issubjected to fractional distillation to remove solvent therefrom as anoverhead product and to obtain a substantially solvent free hydrocarbonbottoms product.

15. The method of claim 12 in which step (1) is conducted at atmosphericpressure and at a temperature within the range from about 20 to about150 C.

16. A method of extracting diaromatic hydrocarbon material from amixture comprising said diaromatic hydrocarbon material and monoaromatichydrocarbon material which comprises: (l) contacting said mixture with amixture of a tertiary amine and monocarboxylic acid whereby an extractphase containing hydrocarbon material -rich lin said diaromatichydrocarbon material, and a rainate phase, are formed and (2)fractionally distilling said extract phase whereby substantially all ofthe tertiary amine-monocarboxylic acid mixture is removed therefrom asan overhead product and substantially all of the diaromatic hydrocarbonmaterial is recovered therefrom as a bottoms product.

17. A method of extracting hydrocarbon material of greater aromaticityfrom a mixture thereof with hydrocarbon material of lesser aromaticitywhich comprises: (l) contacting said mixture with a solvent comprising asubstantially amide-free mixture of tertiary amine and an organic acidselected from the group consisting of carboxylic and sulfonic acidscontaining a minor amount of water, to form an extract phase containinghydrocarbon material rich in said hydrocarbon material of greateraromaticity, and a raffinate phase.

18. The method of claim 17 in which the water is present in the solventin an amount from about 2 to about percent by weight thereof.

19. In the method of extracting aromatic hydrocarbon material from amixture thereof with nonaromatic hydrocarbon material which comprisescontacting said mixture with a solvent for the aromatic hydrocarbonmaterial to form an extract phase containing hydrocarbon material nichin said aromatic hydrocarbon material, and a raffinate phase, theimprovement which ycomprises employing a substantially amide-freemixture `of a tertiary amine and an organic acid selected from the groupconsisting of carboxylic and sulfonic acids as the solvent for thearomatic hydrocarbon material.

20. A method of extracting naphthalene and alkyl naphthalenes from afeedstock containing those compounds and close-boiling mono-aromatichydrocarbons comprising: (l) continuously contacting said feedstock, incountercurrent relationship, with a solvent consistingof a mixture ofacetic acid and triethylamine at a molar ratio of the acid to the amineof from about 1:1 to about 6:1, whereby an extract phase rich in saidsolvent and. containing a portion of Vthe feedstock enriched innaphthalene and alkylnaphthalenes, and a rainate phase containingsubstantially all of the remaining portion of the feedstock and a minoramount of said solvent, are obtained', (2) subjecting the extract phasefrom step (1) to fractional distillation to form an overhead product ofsubstantially pure solvent and a hydrocarbon bottoms product enriched innaphthalene and alkylnaphthalenes; (3) condensinfy the overhead solventproduct from step (2); and (4) recycling the condensed solvent from step(3) to step (l).

References Cited by the Examiner UNITED STATES PATENTS 2,035,102 3/1936Stratford et al, 208-324 2,096,725 10/1937 Andrews et al. 208-3312,191,767 2/1940 McClure et al. 208-331 2,812,372 11/1957 Walsh et al.260-674 2,842,484 7/1958 Fleck 208-330 3,082,270 3/1963 MicKinnis260-674 DELBERT E. GANTZ, Primary Examiner.

MILTON STERMAN, ALPHONSO D. SULLIVAN, Examiners.

I. H. HALL, C. E. SPRESSER, Assistant Examiners.

1. A METHOD OF SEPARATING HYDROCARBON MATERIAL OF GREATER AROMATICITYFROM A MIXTURE THEREOF WITH HYDROCARBON MATERIAL OF LESSER AROMATICITYWHICH COMPRISES CONTACTING SAID MIXTURE WITH A SUBSTANTIALLY AMIDE FREESOLVENT COMPRISING A MIXTURE OF A TERTIARY AMINE AND AN ORGANIC ACIDSELECTED FROM THE GROUP CONSISTING OF CARBOXYLIC AND SULFONIC ACIDS.